Attrition resistance is an important aspect of fluidizable particles, such as catalysts, sorbent materials, reaction surface supports and the like. Fluidizable particles in fluidized beds are used in numerous chemical conversion applications, including catalytic conversions, absorption reactions, and the like. These materials are needed for numerous fluidized bed reactor (FBR) and slurry bubble column reactor (SBCR) based processes where attrition can be a problem severe enough to cause very poor process economics, and in some cases, shut down of commercial processes. Examples of such processes include hot coal gas desulfurization using transport or bubbling-bed reactors, Fischer-Tropsch Synthesis using SBCRs, and flue-gas desulfurization using fluidized-bed reactors.
Fluid catalytic cracking (FCC) is a particularly well known and widely used process that relies on attrition resistant fluidizable catalysts. In this process, a heavy oil or similar hydrocarbon fraction is treated in a riser (transport) reactor with a particulate, attrition resistant aluminosilicate catalyst to "crack" the oil into smaller hydrocarbon chains, which are used to produce gasoline, heating oil, and the like. The catalyst rapidly cokes up in the riser reactor. It is then cyclically removed and heated in a bubbling-bed regenerator in the presence of oxygen. This removes the coke/carbon accumulated on or in the pores of the catalyst. The catalyst is thereafter recycled to the riser for use in the fluid catalytic cracking operation.
In practice, there is a limit to regeneration of FCC catalysts because regeneration can only remove the coke. See e.g., R. Hughes, Deactivation of Catalysts, Academic Press, New York, 1984. After repeated cycles of regeneration and reuse, the catalyst becomes unusable because of heavy metals primarily, nickel and vanadium, that accumulate on the surface and within the pores of the catalyst and interfere with the fluid catalytic cracking operation. Approximately 1000 tons/day of fresh FCC catalyst are used in petroleum refineries worldwide. From this approximately 500 tons/day of spent FCC catalyst are produced that need to be disposed of. Only 5% of this finds reuse in such applications as recycle for refinery as E-Cat, cement, asphalt, and brick. The remainder is disposed of by landfill.
Leachability tests applied to fresh, spent, and demetallized FCC catalyst, FCC catalyst fines, and bricks made by incorporating 5 weight % spent FCC catalyst confirms that a hazardous designation for these solids is not currently warranted. Nevertheless, concerns about the leachability of the spent FCC catalysts continues to be expressed R. Schmitt, Oil and Gas Journal, Nov. 18 p.101 (1991); Environmental Reporter, U.S. Bureau of Nat. Affairs, p.310 (1992)!.
Various processes have been proposed for regenerating heavy metal contaminated catalysts for reuse in the FCC process itself by treating the catalyst with an agent to demetallize or passivate heavy metals accumulated on the surface of the catalyst. For example, U.S. Pat. No. 4,207,204 to McKay et al. teaches treating a spent FCC catalyst with a crude antimony compound to passivate metals on the surface thereof, including vanadium, iron and/or nickel. U.S. Pat. No. 4,485,183 to Miller et al. teaches regenerating a spent FCC catalyst by treating the catalyst with a phosphorous compound. U.S. Pat. No. 4,954,244 to Fu et al. teaches reactivating a spent, metal contaminated FCC catalyst by contacting the catalyst with a dissolved ammonium compound, a fluorine compound, and a passivating agent, preferably magnesium, calcium, boron, aluminum, phosphorous, and/or antimony. Elvin and Pavel Oil and Gas Journal, p. 94, Jul. 22 (1991)! describe an elaborate process named DEMET for metal reclamation from spent FCC catalyst involving calcining, sulfiding, chlorination, drying and recycling of the demetallized FCC catalyst to the FCC process.
Other proposals for regenerating spent FCC catalysts for use in the FCC process involve treating the spent catalyst with metals selected from groups IA and IIA of the Periodic Table of Elements. For example, U.S. Pat. No. 5,021,145 to Chapple teaches regenerating catalysts contaminated with vanadium by treating the catalyst with heavier alkaline earth metal oxides. U.S. Pat. No. 5,260,240 to Guthrie et al. teaches demetallizing the spent FCC catalyst with calcium or magnesium containing additives such as dolomite and sepiolite in an external reactor at 730.degree. C. in the presence of steam. U.S. Pat. No. 5,154,819 to Clark et al. teaches regenerating catalysts by impregnating a spent FCC catalyst with a group IIA metal. U.S. Pat. No. 5,389,233 to Senn teaches regeneration of a spent FCC catalyst by treatment with a lithium containing compound.
Attempts are also being made to develop processes for separation of the potentially active and inactive particles for the FCC process from the spent FCC catalyst using magnetic separation and other techniques. U.S. Pat. No. 5,250,482 to Doctor teaches separation of spent FCC catalyst into several zones with differing levels of nickel, with the portion with the least amount of nickel being recycled back to the FCC unit. U.S. Pat. No. 5,286,691 to Harandi et al. teaches the addition of a metal getter additive to the FCC regenerator with a higher settling velocity. The metals are removed in this process by solid-solid interaction. The additive with the adsorbed metal is withdrawn from the lower portion of the regenerator.
Direct reuse (with no treatment) of spent FCC catalyst for milder cracking and less severe refinery operations has been suggested. For example, U.S. Pat. No. 4,276,150 to McHenry teaches the direct use of spent FCC catalyst for hydrocracking heavy oils and residues. U.S. Pat. No. 5,324,417 to Harandi teaches a process in which spent FCC catalyst is used for demetallizing and deemulsifying refinery sludge and slop oils. U.S. Pat. No. 5,372,704 to Harandi and Owen teaches the use of spent FCC catalyst for recracking of naphtha fractions to lighter products and improve the octane number of the cracked naphtha.
Despite these and numerous other proposals for regenerating and/or reactivating spent FCC catalyst, some 475 tons/day of spent FCC are still disposed of by landfill operations. With growing environmental concern, land filling is becoming more costly and increasingly less desirable.